1. Field of the Invention
The present invention relates to routing techniques with Quality of Service (QoS) support, and more particularly to a routing technique for use in a connectionless network including a connection-oriented network and a router connecting the connectionless network and the connection-oriented network.
2. Description of the Related Art
A routing information notifying method with QoS support has been used to exchange link resource information between routers in an IP (Internet Protocol) network, which is described in Internet Draft (September. 1997) identified by xe2x80x9chttp!/www.ctron.com/support/internet/Internet -Drnat/draft-zhang-qos-ospf-01. txtxe2x80x9d. More specifically, In the IP network composed of a plurality of routers connected through links, the routers can exchange topology information and link resource information for each link with one another. The link resource information includes information of the resources available and information of the resources which have boon reserved. Therefore, each router can obtain the link resource information between any two of all the routers within the IP network.
On the other hand, there has been proposed a routing technique for use in a network composed of IP network and ATM network. For example, In Japanese Patent Unexamined Publication No. 07-250081, a path management method in ATM-LAN network. More specifically, in an ATM-LAN network composed of a plurality of routers and ATM switches which are connected through a permanent virtual circuit (PVC) established based on ATM interface, a path control server is provided which includes an information managing means and an information setting means. The information managing means manages path management information consisting of the routing information for each router and the connection information for each ATM switch. The information setting means outputs the routing and connection information to each router and ATM switch through connection lines to register them onto them. When the network configuration of the ATM-LAN network is changed, path management information 1S updated and new routing information and connection information which arc used to set routers and ATM switches which should change in setting information are obtained from the updated path management information In this prior art, all the routers and ATM switches are managed in a unified way to allow easy and efficient maintenance thereof.
As another example, a router which allows frame transfer efficiency to be improved in a network composed of an IP network including an ATM network is disclosed in Japanese Patent Unexamined Publication No. 10-164119.
In such a network composed of IP network and ATM network, especially a network composed of an IP network including an ATM network, the QoS routing as described before develops some problems. The details will be described with reference to FIG. 1.
As shown in FIG. 1, assuming that a network is composed of an IP network 1 including an ATM network 2. The IP network 1 is composed of a plurality of routers 101-104 connected through links 111-113 and 115 and the ATM network 2. The ATM network 2 is composed of a plurality of ATM switches (not shown). As described above, the routers 101-104 can exchange topology information and link resource information for each link with one another according to routing protocols 121-125 Therefore, each router can obtain the link resource information between any two of all the routers within the IP network.
In this example, the routers 102 and 104 are connected through a virtual circuit (VC) 21 which is initially established in the ATM network 2. In such a network, the default VC 21 is used as a link connecting the routers 102 and 104. Therefore, as to link resource information between the routers 102 and 104, the IP network 1 is notified about only the link resource information of the default VC 21.
In the conventional routing information notifying method, however, even when the link resource of the default VC 21 does not meet the QoS needs, the IP network 1 is notified about only the link resource information of the VC 21. Further, even when there Is another route available in the ATM network 2, the IP network 1 is notified about only the link resource information of the default VC 21. Therefore, the IP network 1 cannot use an available route other than the default VC 21 in the ATM network 2, resulting in reduced efficiency of tho network.
In the case where the IP network 1 is notified about the link resource information of all possible alternative routes in the ATM network 2, a large amount of information is transferred In the IP network 1, which may increase transaction load on routers. Especially, in the case of a large scale ATM network, it becomes difficult to realize the conventional routing information notification. Further, most of the routing information to be transferred are not used actually. Therefore, it is very important to determine how to notify the IP network about the link resource information of the alternative routes in the ATM network.
It is an object of the present invention to provide a quality-ensuring routing method and a router, which are capable of improving the efficiency of a network composed of a connectionless network including a connection-oriented network.
It is another object of the present invention to provide a quality-ensuring routing method and a router, which are capable of efficiently notifying a connectionless network about link resource information of a connection-oriented network.
It is still another object of the present invention to provide a routing information notifying method and a router, which are capable of notifying a connectionless network about necessary link resource information of possible alternative routes existing in a connection-oriented network.
According to the present invention, in a network composed of a connectionless network including a connection-oriented network, wherein at least two routers are connected to each other through a virtual circuit established in the connection-oriented network, the connectionless network is notified about link resource Information of the connection-oriented network in such a way that an alternative route to the virtual circuit in the connection-oriented network is searched For and the connectionless network is notified about a link resource of the alternative route found in the connection-oriented network.
The connectionless network may be notified about link resources of all alternative routes found in the connection-oriented network.
Preferably, a link resource of each route in the connection-oriented network is computed and an alternative route satisfying required quality is searched for based on the link resource of each route.
Further preferably, a link resource of each route in the connection-oriented network is computed and an alternative route having a link resource exceeding a link resource of the virtual circuit is searched for based on the link resource of each route.
According to another aspect of the present invention, the connectionless network is notified about link resource information of the connection-oriented network in such a way that when the link resource of the virtual circuit satisfies required quality, the connectionless network is notified about only the link resource of the virtual circuit and, when the link resource of the virtual circuit does not satisfy the required quality, an alternative route to the virtual circuit in the connection-oriented network is searched for, and then the connectionless network is notified about a link resource of the alternative route found in the connection-oriented network.
Preferably, a link resource of each route in the connection-oriented network is computed and then an alternative route satisfying required quality is searched for based on the link resource of each route.
Further preferably, a link resource of each route in the connection-oriented network is computed and then an alternative route having a link resource exceeding a link resource of the virtual circuit is searched for based on the link resource of each route.
Furthermore preferably, a link resource of a previously selected route in the connection-oriented network is computed and then an alternative route satisfying required quality is searched for based on the link resource of the previously selected route. In this searching step, an alternative route having a link resource capable of covering a short fall of the virtual circuit in link resource is preferably searched for.